Why do people still watch traditional TV shows? If you think really hard about any show out now, you could replace a few characters and it was the same thing you grew up watching. Familiarity. The writers might twist things slightly but they stick to what has always worked. This is not a slight on TV writers at all. The stress of coming up with something original with such constraints would be maddening.
Fiction writers have fallen into a similar mode and only a few breakouts deviate from the course. The goal is to be famous, make millions, get on talk shows, etc. Every writer has a dream. The piled up rejection letters (even the ones with the nice handwritten note at the bottom) build this conformity.
The part that publishers forget too often, that it is the offbeat but well written that become household words and sometimes their own genre’s. Written word and stories have lived for millennia and yet Dystopian wasn’t a thing, let alone a genre until 1924, when it was first termed anti-utopian. That sure rolls off the tongue better. If something can be added to writing as a whole in the last few relative seconds of a forty-five century old tradition then there is still new ground to explore. If you want fame and glory write the latest werewolf meets vampire drama for young adults. There is nothing wrong with that. If you, however, wish to chart a new path and maybe write something worth imitating. Be prepared for more rejection slips than you will ever know what to do with.